The present invention relates to tongs for seizing bones or bone fragments and to a device for external fixation of bone.
In addition to conventional external fixation means, which fixate the bones with screws or nails, other devices use bone clamps to fixate bones or bone fragments. The advantages of clamping fixation systems that use bone clamps include: (1) the lower risk of infection otherwise caused by germ invasion along the nails or screws and into the bone; and (2) less interference with blood flow through the bone, such blood flow being substantially hampered when introducing nails or screws.
A device for the fixation of bones or bone fragments is known from published French patent application No. FR 1,169,404 of MONTEZIN. This known device comprises two or more forceps-like instruments to fasten the bone fragments. At the rear end of one of the forceps levers, a rod with teeth is attached such that an additional set of teeth at the rear end of the other forceps lever is engageable and fastenable with the rod to clamp a bone fragment between the tips of the forceps-like instrument. Additionally, a clamp is connected to one of the forceps levers for coupling the instrument with a longitudinal rod by means of a threaded rod and a second clamp. At the longitudinal rod two or several forceps-like instruments are attachable in the same manner. Disadvantages of this design include the decreased stability of the device due to the displaceability and the complicated configuration of the clamps and threaded rod.
A bone clamping forceps for clamping a bone or bone fragment is also known from published Swiss patent application No. CH 607,915 of Sythes AG Chur. This known bone clamping forceps comprises two forceps levers that are fastenable relative to each other by means of a threaded rod. This threaded rod is pivotably connected to one of the forceps levers and is accepted within a bore hole through the other forceps lever. The forceps levers are fastened by means of a nut which is screwable onto the threaded rod. However, this bone clamping forceps lacks any means to connect with another bone clamping forceps. Therefore, additional connection means would have to be attached when required.
European patent application No. 0,457,017 of Synthes AG Chur discloses a clamp fixation system whereby the bone is seized by the tips of bone tongs instead of being gripped by a screw or a nail. This feature offers the advantage that no drilling through the bone is needed, thereby eliminating heat-induced necroses. Furthermore, blood circulation is only minimally impaired. Several such bone tongs can be externally joined together in a way similar to the case of screws and nails. However, the same mechanism used to lock the tongs and to connect several bone tongs together as an external bone fixation device are both configured in the articulation of the bone tongs. This makes the articulation bulky and complex.
Thus, a need exists for improved bone tongs.
The present invention is directed to simple and manually operable repositioning tongs (or bone grasping tongs) for non-invasive temporary fixation of bone fractures. In addition, two or more of these repositioning tongs can be connected within an external fixation device to fixate bone fractures. In other words, the present invention is directed to both tongs for seizing bone or bone fragments and a device for externally fixating bone fractures.
The repositioning tongs of the present invention comprise two tongs levers joined by a connector or coupler so as to be mutually pivotable about an axis of rotation. The two tongs levers have clamping tips at their ends which serve to seize the bone. Furthermore, a locking means or locking element detachably compresses the tongs levers against each other and locks the tongs levers. Also, a connecting member, such as a connecting bolt, allows the tongs to be connected to another element of an external fixation device. The locking means is located at a first distance from the axis of rotation, whereas the connecting bolt is located at a second distance from the axis of rotation. The longitudinal axis of the connecting bolt is in the plane of pivoting of the tongs levers.
The second distance, which is between the axis of rotation and the connecting bolt, and the first distance, which is between the axis of rotation and the locking means, may be of the same magnitude. Preferably, however, the second distance is smaller than the first distance to preclude large levers between the clamping tips, which seize the bone, and the connecting bolt. Otherwise, large torques might arise in the connecting bolt. On the other hand, the first distance is preferably large so that excessively high stresses in the locking means caused by the clamping force of the repositioning tongs is precluded.
The connecting means pivotably joining the two tongs levers is preferably in the form of a screw threaded into one of the tongs levers and rotatably supported in the other tongs lever. The connecting bolt is cross-sectionally circular-cylindrical.
The locking means is preferably in the form of a tightening screw, which is firmly joined to one of the tongs levers, and a nut which is to be threaded on the screw. By means of an elongated slot, the tightening screw can be displaced in and along the other tongs lever so the levers can be opened and closed. Moreover, the nut may be conically shaped at its end, resting against the tongs lever.
In another embodiment, the locking means may be a clamp moveable into different positions and a serrated rod mounted on the inside of the second tongs lever. The clamp detachably engages the serrations. The serrations are such that, when the tongs levers are forced together, the clamp automatically enters the serrations on the rod. In order to release the locked tongs, the clamp is loosened by hand, namely by switching the clamp into a position at which the serrations at the shaped rod are disengaged.
In another aspect of the present invention, the external fixation device for externally fixating bone fractures comprises at least one repositioning tongs, at least one elongated support, and at least one clamp detachably connecting in mutually rotatable manner the connecting bolt of a repositioning tongs and an elongated support. The clamp consists of two clamp elements mutually rotating about an axis of rotation, each clamp element comprising a continuous cylindrical borehole. These boreholes may be of a circular-cylindrical cross-section corresponding to the cross-section of the connecting bolt and of the elongated support. The axis of rotation about which the two clamps are mutually rotatable is perpendicular to the plane subtended by the two longitudinal axes of the boreholes. By means of a tightening screw, which is concentric with the axis of rotation and which passes through the boreholes in the clamps, the two slotted clamps can each be compressed and can be simultaneously forced against each other. As a result, the connecting bolt of the repositioning tongs is clamped in one clamp and the elongated support is inserted in the borehole of the other clamp. The connecting bolt and the elongated support are thus locked in these clamps. Simultaneously, the mutually rotatable clamps can be affixed in a selected relative position. To better lock the two clamps against rotation, the two abutting end faces of the clamp elements are fitted with mutually engaging serrations.
With the reposition tongs of the present invention, the force exerted by the tongs levers and the position of the repositioning tongs within the external fixation device can be adjusted independently from each other because the connecting bolt is away from the axis of rotation of the repositioning tongs and because the connecting bolt is independent of the locking means. Due to the separation of the connecting means, the locking means, and the axis of rotation, the axis of rotation assumes a simple and compact configuration.